Mail RFCs (1)

Mail RFCs (2)

Message Header RFC5322 (obsoletes RFC5322)
MIME 1 Body Format RFC2045
MIME 2 Media Types RFC2046
MIME 3 Header Extension RFC2047
MIME 4 Registration RFC4289 (旧 RFC2048)
MIME 5 Examples RFC2049

SMTP Server

Session Initialion

C->S Connect TCP 25
S->C 220 greeting message

Client Initiation

C->S EHLO Client Identiy
S->C 250 Server Idenity + ESMTP Capabilities

Mail Transactions (1)

C->S MAIL From: sender
S->C 250 Ok
C->S RCPT To: recipient
S->C 250 Ok

Mail Transactions (2)

C->S DATA
S->C 354 End data with .
C->S (message)
C->S .
S->C 250 Ok

Session Close

C->S QUIT
S->C 221 Bye

Debugging Commands

EXPN ... Expand (list address)
VRFY ... Verify (e-mail address)
almost always disabled

SMTP Relay

Relay to internal SMTP servers
Relay to non-IP email system
- Historical ... @BITNET
- X.400 MHS
From internal users to the Internet

Received headers

When forwarding a message, a gateway MUST prepend a Received: line
but it MUST NOT alter in any way a Received: line that is already in the header section.

Other SMTP Commands

HELO ... Older EHLO
RSET (reset)
HELP/NOOP

SMTP Response Code (1)

2yz ... Positive Completion reply
3yz ... Positive Intermediate reply
4yz ... Transient Negative Completion reply
5yz ... Permanent Negative Completion reply

SMTP Response Code (2)

x0z Syntax related
x1z Informational
x2z Connections related
x5z Mail system related

Reply continuation

Example:

   250-First line
   250-Second line
   250-234 Text beginning with numbers
   250 The last line

Command-Reply Sequences

See RFC5321

Size and Timeouts

See RFC5321

Locating Servers

DNS MX record
or A/AAAA record

SMTP Authentication

SMTP AUTH (PLAIN)
C->S AUTH PLAIN (base64 encoded auth info)
S->C 235 2.7.0 Authentication successful
use STARTTLS (TLS)

Outbound Port 25 blocking

ISP users can send Spam directly to an outer SMTP server
Prevent this by blocking TCP port 25
Mobile users can use mail submission agent (port 587) with authentication

Quiz of the day

What is the number of TCP port in following message agents
Message Transfer Agent
Message Submission Agent

Homework

Use "telnet is01 25" to connect our mail server and send yourself an e-mail message.
Record the transaction and view the source of the message you've received.
Include both the transaction and the message source in your report.

Simple Mail Transfer Protocol

Tokio Kikuchi

Mail RFCs (1)

Mail RFCs (2)

SMTP Server

Session Initialion

Client Initiation

Mail Transactions (1)

Mail Transactions (2)

Session Close

Debugging Commands

SMTP Relay

Received headers

Other SMTP Commands

SMTP Response Code (1)

SMTP Response Code (2)

Reply continuation

Command-Reply Sequences

Size and Timeouts

Locating Servers

SMTP Authentication

Outbound Port 25 blocking

Quiz of the day

Homework